I’m running a pair of 500GB LaCie drives in RAID 1 set that got out of sync recently during a hardware failure that resulted in Apple replacing my logic board. I first noticed this because Disk Utility listed my RAID set as ‘degraded’. Simple enough to fix, I thought, and clicked the Rebuild button. Wrong.

Turns out there is a bug in Leopard’s Disk Utility whereby you must use the command line to rebuild degraded RAID sets. If you are getting the infamous ‘Unrecognized Filesystem’ error when you try to rebuild your RAID set follow the instructions below.

1. Erase the RAID disk storing degraded slice in Disk Utility. It will be the one labeled in red.
2. Open up Terminal. Run:

   diskutil checkRAID

   you will see something like this:

   RAID SETS
   ---------
   ===============================================================================
   Name:                 thriller
   Unique ID:            B63E8B4C-97D7-4A90-960B-B5DCB9030731
   Type:                 Mirror
   Status:               Degraded
   Size:                 499972669440 B
   Device Node:          disk3
   Apple RAID Version:   2
   -------------------------------------------------------------------------------
   #   Device Node       UUID                                   Status
   -------------------------------------------------------------------------------
   0   -none-            68269FE2-0C68-4C2D-B129-FFF1DA5999EC   Missing/Damaged
   1   disk1s3           108564B3-F353-4740-BF21-72F89E881E46   Online
   ===============================================================================

   Note the RAID’s Unique ID. (in this case it’s B63E8B4C-97D7-4A90-960B-B5DCB9030731)

3. Next run:

   diskutil list

   it will spit out something like:

   /dev/disk0
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:      GUID_partition_scheme                        *111.8 Gi   disk0
      1:                        EFI                         200.0 Mi   disk0s1
      2:                  Apple_HFS dangerous               111.5 Gi   disk0s2
   /dev/disk1
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:     Apple_partition_scheme                        *465.8 Gi   disk1
      1:        Apple_partition_map                         31.5 Ki    disk1s1
      2:                 Apple_Boot Boot OSX                128.0 Mi   disk1s2
      3:                 Apple_RAID                         465.6 Gi   disk1s3
   /dev/disk2
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:     Apple_partition_scheme                        *465.8 Gi   disk2
      1:        Apple_partition_map                         31.5 Ki    disk2s1
      2:                  Apple_HFS Untitled                465.6 Gi   disk2s3
   /dev/disk3
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:                  Apple_HFS thriller               *465.6 Gi   disk3
   

   here we are looking for the Identifier of the freshly erased drive. (in this case it is disk2s3)

4. The last step is to run

   diskutil addToRAID member <drive identifier> <RAID Unique ID>

   so for me the command looks like:

   diskutil addToRAID member disk2s3 B63E8B4C-97D7-4A90-960B-B5DCB9030731

5. Hold on tight. When I ran the command above I got a progress window indicating that the rebuild process would take 18 hours. It actually took 22 hours. If you don’t get the progress window you can check the progress with

   diskutil checkRAID

Hopefully this saves you a bit of trouble. This is the second time my RAID set has been degraded and I’m beginning to doubt the wisdom of running software RAID at all but for now I’m back on the horse.

This entry was posted on Sunday, July 20th, 2008 at 6:55 pm and is filed under Advanced Backup, Macintosh, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.